Gene networks in the embryo and endometrium related to embryo survival

Low fertility is one of the major problems limiting the efficiency of the dairy industry. Successful pregnancy establishment and development to term depend on the suitability of the endometrial environment and the intrinsic quality of the embryo. Accurate assessment of both, however, is challenging. Therefore, the present survey reviews current knowledge of the molecular networks in the endometrium related to pregnancy establishment and maintenance to term. Accordingly, distinct molecular signatures of the bovine endometrium, elucidated by innovative approaches, could be correlated with pregnancy success. However, not only must the reproductive tract provide a suitable environment but the embryo itself must be competent to express its developmental program. Numerous studies have correlated molecular networks of bovine embryos with their developmental capacity. However, most studies were, by their nature, invasive and the findings were therefore difficult to extrapolate beyond the developmental stages examined. Hence, a second aim is to present new strategies employing embryo biopsies for a direct connection between molecular signatures and embryo developmental capacity. Large scale differences, at the molecular level, were reported for blastomeres whose counterparts developed to the blastocyst stage compared to those with lower developmental competence, thus unraveling distinct molecular fingerprints related to ability to develop to the blastocyst stage. Similarly, distinct molecular signatures at the blastocyst stage were associated with embryo developmental competence to term. In summary, further understanding of molecular signatures related to endometrial receptivity and embryo developmental capacity has been gained from novel innovative strategies including embryo microdissection as well as by examining endometrial samples collected in the cycle preceding the one in which conception occurs.